1. Field of the Invention
The present invention relates to a micro film reader for projecting on a viewing screen a micro image in a micro film capable of recording various kinds of information in high density, and more particularly to the micro film reader including a film carrier for holding the micro film having micro images printed in two channels provided in the width direction of the film and a carrier shifting device for shifting the film carrier in the width direction of the micro film.
2. Description of the Prior Art
A known carrier shifting device included in the above-described micro film reader comprises a manual control apparatus such as a knob and a handle and the like and a linking mechanism for operatively connecting the manual control apparatus and the film carrier. In switching the channels, an operator has to change relative positions of the film and the viewing screen by controlling the manual control apparatus to shift the film carrier in the width direction of the film with the operator watching the micro image projected on the viewing screen.
However, according to this system, the operator has to manually operate the manual control means to shift the film carrier when projecting on the viewing screen the desired micro image recorded in a different channel from the channel of the presently projected micro image. Moreover, the operation of the manual control means must be carried out carefully in order to completely project the desired micro image on the viewing screen by adjusting the relative positions of the film and the screen. Thus, the projecting operation of the micro image is not carried out efficiently.
U.S. Pat. No. 4,436,391 discloses another arrangement comprising a drive apparatus for the carrier shifting device and channel switching means for actuating the drive apparatus to automatically permit the entire micro image in the width direction of the micro film recorded in a channel different from the currently projected channel to be shifted into a desired position on the viewing screen, whereby the channel switching operation may be carried out more readily.
However, the micro film reader employing this arrangement has a problem to be described hereinafter.
Distance between the micro images `IA` and `IB` respectively recorded in the two channels, as illustrated in FIG. 4-b or FIG. 4-d, is not always the same depending on a make of the employed film `F`. Also, the micro images `IA` and `IB` are not always printed linear-symmetrically relative to the width direction of the film `F`. This is because different manufacturers employ different standards in printing the micro images `IA` and `IB`.
As a result, the micro image of either of the channels may be entirely projected on the screen in the case of a certain make of the micro film. However, when the micro film of a different make is employed, the micro image(s) of either of or both of the channels may fail to be completely projected.
In order to permit the entire micro images of both of the channels to be projected on the viewing screen in the above-mentioned case, the film carrier must be shifted mannually or a fine adjustment on the printed board must be made each time the film recorded by a different image-printing standard is used.